Method of conversion of a drilling mud to a gel-based lost circulation material to combat lost circulation during continuous drilling

ABSTRACT

A method of conversion of a water-based mud to a gel-based LCM quickly to control lost circulation in a lost circulation zone in a wellbore during continuous drilling with a drilling mud, the drilling mud comprises a volcanic ash, water, a de-foamer, a pH buffer, and a polymer. The method comprises the steps of entering the lost circulation zone, determining a lost circulation volumetric flow rate, metering a first amount of a binder into the drilling mud to create a binder containing mud, pumping the binder containing drilling mud into the wellbore, and suspending metering of the first amount of the binder to the drilling mud after a pre-defined regulating period of time effective to permit the binder containing drilling mud to create a gel-based LCM operable to alter the lost circulation zone.

BACKGROUND

Field of the Invention

Embodiments of the invention generally relate to methods to control lostcirculation in a lost circulation zone in a wellbore during continuousdrilling with a drilling mud. More specifically, embodiments of theinvention relate to methods for converting a drilling mud into agel-based LCM (lost control material) composition during continuousdrilling.

Description of the Related Art

Lost circulation is one of the frequent challenges encountered duringdrilling operations. Lost circulation, which can be encountered duringany stage of operations, occurs when drilling fluid (or drilling mud)pumped into a well returns partially or does not return to the surface.While some fluid loss is expected, fluid loss beyond acceptable norms isnot desirable from a technical, an economical, or an environmental pointof view. About 75% of the wells drilled per year encounter lostcirculation problems to some extent. Lost circulation is associated withproblems with well control, borehole instability, pipe sticking,unsuccessful production tests, poor hydrocarbon production after wellcompletion, and formation damage due to plugging of pores and porethroats by mud particles. In extreme cases, lost circulation problemsmay force abandonment of a well. In addition, delays in controlling lostcirculation can lead to highly complex problems, including the failureto control the lost circulation in any meaningful way.

Billions of dollars are lost per year due to lost circulation indrilling operations. Lost dollars are due to losses of drilling fluids,losses of production, and the costs of lost circulation materials (LCMs)used in combating lost circulation.

Lost circulation can cause environmental problems if drilling muds orLCMs interact with the environment surrounding the reservoir.Conventional LCMs pose a risk to sensitive environments, such as marineenvironments because they are not biodegradable and can be toxic tomarine life. Public awareness of drilling operations, including thedrilling fluids used, has contributed to demands from environmentalregulatory bodies to develop biodegradable and virtually non-toxic LCMs.

Lost circulation can be categorized as seepage type, moderate type,severe type, and total loss, referring to the amount of fluid or mudlost. The extent of the fluid loss and the ability to control the lostcirculation with an LCM depends on the type of formation in which thelost circulation occurs. Formations with low permeability zones, i.e.,those with microscopic cracks and fissures, usually have seepage typelost circulation. Seepage type lost circulation experiences a loss ofless than 10 bbl/hour for water based drilling muds, or about 10 bbl/hrfor oil based drilling muds. Formations with narrow fracture sizes andlower fracture density usually trigger a moderate loss of drilling mud.A moderate type lost circulation experiences a loss at a rate in therange of about 10 bbl/hr to about 100 bbl/hr. Formations with highpermeability zones, such as super-K formations, highly fracturedformations with large fracture sizes and high fracture density, oftenexperience very high mud loss with a drastic increase in total mud andmud management costs. A severe type lost circulation experiences lossesof greater than about 100 bbl/hr. Formations with inter-connectedvugular and cavernous zones or formations with induced inter-vugularconnection often cause massive loss of drilling mud with no return ofcirculation. It is possible for one wellbore to experience all of thesezones.

Other formations may experience lost circulation if an improper mudweight is used while drilling. Such formations include narrow mud weightwindow, low fracture gradient, depleted reservoir pressure, formationswith soluble minerals such as halite, evaporate, and anhydrite.

In general, seepage type and moderate type losses occur more frequentlythan severe type lost circulation. In the Saudi Arabian fields, however,the formations encountered while drilling reservoir and non-reservoirsections have unique depositional histories and matrix characteristicsthat make the super-K, fractured, vuggy, cavernous, faultedcharacteristics of the carbonate rock formations prone to moderate tomassive loss of drilling fluid. Some of the losses are so massive thathundreds of barrels of mud are lost in an hour with no return of fluidto the mud return line, as the rate of loss usually exceeds the rate ofreplacement of drilling mud. Thus, even though the frequency of severelost circulation is less than seepage or moderate lost circulation,severe lost circulation has a significant economic impact on drillingoperations.

LCMs are used to mitigate the lost circulation by blocking the path ofthe fluid. The type of LCM used in a loss circulation situation dependson the extent of lost circulation and the type of formation.Conventional LCMs, currently available in the industry, includeparticulates, flaky materials, granular materials, and gel LCMsincluding cross-linked gels, cross-linked polyacrylamrides,polyacrylates, super absorbing polymers (SAP), or a combination of theabove. Conventional gel LCMs typically contain one or more polymers, oneor more monomers, one or more cross-linkers, including chemicalcross-linkers, a cross-linking initiator, and a fluid phase, such aswater or oil. Some formulations may include particles.

For zones experiencing seepage type to moderate type lost circulation,conventional LCMs that include particulates, flakes, gels and/or acombination are often effective in controlling the loss zones. Polymericand gel LCMs are also commonly used to control moderate to severe lossof circulation, due to their ability to swell, gel, crosslink, and/orexpand. For example, SAPs expand many times in volume in the presence ofwater. The swelling, gelling, crosslinking, and/or expansion of the LCMshelps to stop the loss of drilling mud by plugging the fractures and/orthe vugs. However, many high permeability zones experience limitedsuccess in attempts to control a lost circulation event, even with theuse of conventional non-gel and gel LCMs. For formations with massiveloss of drilling mud, current chemical methods of loss control rarelywork.

Poor control in a lost circulation zone is often due to the LCM itself.The efficacy of a gel LCM depends in large part on the fracturedimensions, but also on the gel characteristics, namely the gelstiffness modulus and the yield strength. The gel stiffness modulus andthe yield strength are indicative of the extent to which the gel LCMresists flow when forces are applied. Gel stiffness modulus is theextent to which a material resists deformation in response to an appliedload, i.e. it is a measure of the rigidity of the material. Yieldstrength is a measure of the strength of a material, it is the forcerequired to initiate plastic deformation. A high gel stiffness modulusand high yield strength indicate a gel that is resistant to deformationand that is therefore likely to solidify into a rigid gel. A gel with alow yield strength and low gel stiffness modulus is likely to form asoft gel system. A soft gel can control seepage type loss zones, butbecause soft gels cannot resist the stresses caused by fluids beingpumped into the formation, a soft gel LCM will continue to move throughthe fractures and channels of moderate to severe loss zones withoutcreating an effective flow barrier. If the gel LCM cannot seal the lostcirculation zone effectively, it may not bring the mud loss below themaximum allowable limit. In some cases, the gel may not be capable ofsolidifying at all. Tests indicate that especially in vugularformations, conventional gel LCMs perform poorly.

Conventional gel LCMs usually have poor thermal stability, chemicalstability, low gel stiffness modulus, low yield strength, and lowtolerance for salt, making them unsuitable for some environments, e.g.,marine, and thus have limited capacity in controlling loss ofcirculation, especially in highly fractured and cavernous formations.

In addition, the formulations of conventional gel LCMs require specialpreparation and handling. Special preparations can include the order inwhich the components are mixed, mixing techniques, or the need forspecialized mixing units. If the formulation guidelines are not followedprecisely, the conventional gel LCM may not obtain homogeneous gelcharacteristics. Careful handling implies the placement and pumping ofthe LCM into the formation. Conventional gel LCMs require preciseplacement in the formation due to the reaction kinetics of the polymersand cross-linkers. Proper placement ensures that the materials reach theproper gel characteristics at the target location. Proper placement inturn depends on the pumping schedule and the pumping units, which oftenmust be highly specialized. In addition, drilling operations are usuallystopped until the lost circulation zone is sealed and fluid losses tothe formation are reduced to an acceptable level.

The requirements for preparation and placement mean that significanttime can lapse between reaching lost circulation and beginning controlmeasures with conventional gel-based LCMs. At a minimum, the time lapsetranslates to a substantial volume loss of drilling fluid. At worst, theextended preparation time may aggravate the problem, turning amanageable lost circulation problem into a situation in which lostcirculation control is not possible and the entire well must beshut-down.

The industry needs an alternative lost circulation treatment that can beprepared quickly to control moderate to high mud losses. Beginning alost control treatment process as soon as possible after the loss zoneis encountered is desirable. A suitable alternative that overcomes thedrawbacks of conventional gel LCMs to combat lost circulation and avoidthe operational complexities associated with delayed lost circulationtreatment is desirable.

A gel-based LCM that shows improved yield strength and gel stiffnessmodulus, and thus effectively mitigates mud loss, reduces volume of LCMpill, and meets environmental regulations is desired.

SUMMARY OF THE INVENTION

Embodiments of the invention generally relate to methods to control lostcirculation in a lost circulation zone in a wellborn during continuousdrilling with a drilling mud. More specifically, embodiments of theinvention relate to methods for converting a drilling mud into agel-based LCM composition during continuous drilling.

In one aspect of the present invention, a method to control lostcirculation in a lost circulation zone in a wellbore during continuousdrilling with a dual-purpose drilling mud is provided. The methodincluding the steps of entering the lost circulation zone, the lostcirculation zone being where a flow rate of the dual-purpose drillingmud that returns to a surface is less than a flow rate of thedual-purpose drilling mud pumped into the wellbore, wherein thedual-purpose drilling mud includes a volcanic ash, water, a de-foamer, apH buffer, a viscosifier, and a fluid loss additive. The method furtherincludes the steps of estimating a lost circulation volumetric flowrate, the lost circulation volumetric flow rate being defined as adifference between the flow rate of the dual-purpose drilling mud pumpedinto the wellbore and the flow rate of the dual-purpose drilling mudthat returns to the surface, metering a first amount of a binder intothe dual-purpose drilling mud to create a binder containing dual-purposedrilling mud, wherein the first amount of the binder metered is in apre-selected range based on a target gel characteristic, such that thefirst amount of the binder metered is operable to achieve the target gelcharacteristic of the binder containing dual-purpose drilling mud,pumping the binder containing dual-purpose drilling mud into thewellbore, and suspending metering of the first amount of the binder tothe dual-purpose drilling mud after a pre-defined regulating period oftime, wherein the pre-defined regulating period of time is effective topermit the binder containing dual-purpose drilling mud to achieve thetarget gel characteristic to create a gel-based LCM for contact with thelost circulation zone, the gel-based LCM being operable to alter thelost circulation zone, such that the flow rate of the dual-purposedrilling mud that returns to the surface increases.

In certain aspects of the present invention, the method further includesthe steps of estimating a second lost circulation volume, the secondlost circulation volume being defined as a difference between the flowrate of the dual-purpose drilling mud pumped into the wellbore after thestep of suspending metering of the first amount of the binder and theflow rate of the dual-purpose drilling mud that returns to the surface,metering a second amount of the binder into the dual-purpose drillingmud, wherein the second amount of the binder metered is in thepre-selected range based on the target gel characteristic, andsuspending metering of the second amount of the binder. In certainaspects of the present invention, the method further includes the stepof mixing the first amount of the binder with the dual-purpose drillingmud in a separate mixing step following the step of metering the firstamount of the binder into the dual-purpose drilling mud. In certainaspects of the present invention, the volcanic ash is a Saudi Arabianvolcanic ash. In certain aspects of the present invention, the pH bufferis selected from the group consisting of sodium hydroxide, potassiumhydroxide, and lime. In certain aspects of the present invention, theviscosifier is XC polymer. In certain aspects of the present invention,the fluid loss control additive is psyllium husk powder. In certainaspects of the present invention, the binder is selected from the groupconsisting of drilling grade cements of Class A, Class B, Class C, ClassG, Class H or combinations thereof. In certain aspects of the presentinvention, the pre-defined regulating period of time is between 30minutes and 2 hours. In certain aspects of the present invention, aweight ratio of the volcanic ash to the binder is 1:1.5 to 1:3. Incertain aspects of the present invention, the target gel characteristicis selected from the group consisting of a gel breaking strength, a gelstiffness modulus, a yield strength, and combinations thereof.

In a second aspect of the present invention, a gel-based LCM compositionis provided. The gel-based LCM composition includes a volcanic ash,water, a viscosifier, a fluid loss control additive, a pH buffer,wherein the pH buffer is operable to adjust a pH of the gel-based LCM, ade-foamer, wherein the de-foamer is operable to reduce the creation offoam, and a binder, wherein the binder is operable to achieve the targetgel characteristic of the gel-based LCM.

In certain aspects of the present invention, the volcanic ash is a SaudiArabian volcanic ash. In certain aspects of the present invention, thepH buffer is selected from the group consisting of sodium hydroxide,potassium hydroxide, and lime. In certain aspects of the presentinvention, the viscosifier is XC polymer. In certain aspects of thepresent invention, the fluid loss control additive is psyllium huskpowder. In certain aspects of the present invention, the binder isselected from the group consisting of drilling grade cements Class A,Class B, Class C, Class G, Class H or combinations thereof. In certainaspects of the present invention, a weight ratio of the volcanic ash tothe binder is 1:1.5 to 1:3.

In a third aspect of the present invention, a method to control lostcirculation in a lost circulation zone in a wellbore using a gel-basedLCM is provided. The method includes the steps of mixing a gel-based LCMpill, the gel-based LCM pill including a volcanic ash, water, aviscosifier, a fluid loss control additive, a pH buffer, wherein the pHbuffer is operable to adjust a pH, a de-foamer, wherein the de-foamer isoperable to reduce the creation of foam, and a binder, wherein thegel-based LCM pill is operable to achieve a target gel characteristic tocreate the gel-based LCM, aligning an open end pipe in proximity to thelost circulation zone, the open end pipe configured to deliver thegel-based LCM pill to the lost circulation zone, and pumping thegel-based LCM pill through the open end pipe at a pill pump rate,wherein the pill pump rate is effective to position the gel-based LCMpill to create the gel-based LCM composition for contact with the lostcirculation zone, the gel-based LCM being operable to alter the lostcirculation zone.

In certain aspects of the present invention, the method further includesthe steps of suspending pumping of a drilling fluid into the wellbore,wherein the step of suspending pumping occurs at a point in time priorto the step of pumping the gel-based LCM pill through the open end pipe,pumping a displacing mud into the open end pipe to displace thegel-based LCM pill from the open end pipe, wherein the step of pumpingthe displacing mud is effective to position the gel-based LCM pill incontact with the lost circulation zone, and shutting the wellbore for agelling time, wherein the gelling time affords the gel-based LCM pilltime to form the gel-based LCM. In certain aspects of the presentinvention, the volcanic ash is a Saudi Arabian volcanic ash. In certainaspects of the present invention, the pH buffer is selected from thegroup consisting of sodium hydroxide, potassium hydroxide, and lime. Incertain aspects of the present invention, the viscosifier is XC polymer.In certain aspects of the present invention, the fluid loss controladditive is psyllium husk powder. In certain aspects of the presentinvention, the binder is selected from the group consisting of drillinggrade cements of Class A, Class B, Class C, Class G, Class H orcombinations thereof. In certain aspects of the present invention, thegelling time is between 30 minutes and 2 hours. In certain aspects ofthe present invention, a weight ratio of the volcanic ash to the binderis 1:1.5 to 1:3.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescriptions, claims, and accompanying drawings. It is to be noted,however, that the drawings illustrate only several embodiments of theinvention and are therefore not to be considered limiting of theinvention's scope as it can admit to other equally effectiveembodiments.

FIG. 1(a)-(f) are pictorial representations of the gel-based LCM duringsuspended weight method.

FIG. 2 is a compression versus displacement curve for a gel-based LCMsample.

FIG. 3 is a compression versus displacement curve for a gel-based LCMsample.

FIG. 4 is a compression versus displacement curve for a conventionallost circulation material sample.

FIG. 5 is a compression versus displacement curve for a conventionallost circulation material sample.

FIG. 6 is a comparison of the gel stiffness modulus between the samplesof the gel-based LCM and the conventional lost circulation materialsamples.

FIG. 7 is a comparison of the yield strength between the samples of thegel-based LCM and the conventional lost circulation material samples.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, which illustrate embodiments ofthe invention. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theillustrated embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

A composition for a gel-based LCM to treat a lost circulation zone isherein provided. The gel-based LCM includes volcanic ash, water, aviscosifier, a fluid loss control additive, a binder, a pH buffer, and adefoamer. The viscosifier and fluid loss control additive surround thevolcanic ash forming a soft coating on the volcanic ash particles. Thebinder is any cement operable to trigger inter-particle soft bonding,networking, and gelling of the volcanic ash, water, viscosifier, andfluid loss control additive to create the gel-based LCM. Without beingbound to a specific theory, the water combines with the hydrophiliccement particles to form calcium silicate hydrate crystals. The calciumsilicate hydrate crystals grow and extend through the surrounding waterphase linking together with the soft-coated volcanic ash particles toform the gel, where the volcanic ash acts as a dispersed filler. Thegel-based LCM is a flexible stiff gel network. The volcanic ash,viscosifier, and fluid loss control additive prevent the gel-based LCMfrom hardening beyond a flexible stiff gel network. In at least oneembodiment of the present invention, the gel-based LCM is in the absenceof a hard gel or solid.

In certain embodiments of the present invention, the volcanic ash isSaudi Arabian volcanic ash. In certain embodiments, the viscosifier isXC polymer. In certain embodiments, the fluid loss control additive ispsyllium husk or psyllium husk powder. In certain embodiments, thebinder is selected from the group consisting of drilling grade cementsthat are used to complete a well after making the borehole. In someembodiments, the cement is a Portland cement (i.e. a hydraulic cement).In some embodiments, the cement is a Portland Cement selected from ClassA, Class B, Class C, Class, G, Class H, or combinations thereof. In atleast one embodiment, the cement is a Class H cement. The pH bufferadjusts the pH of the drilling mud. A target pH reduces the corrosioneffects on the subsurface tools. The target pH range is between about 8and about 11, alternately between about 8.5 and about 10.5, andalternately between about 9 and about 10. In certain embodiments, the pHbuffer is selected from the group consisting of sodium hydroxide,potassium hydroxide, and lime. In at least one embodiment, the pH bufferis sodium hydroxide. The de-foamer readily reduces the tendency of thedrilling mud to foam. In at least one embodiment, the de-foamer is abrine. In at least one embodiments, the de-foamer is BARABRINE® defoam.BARABRINE® defoam is a liquid blend of nonionic surfactants.

In at least one embodiment of the present invention, the gel-based LCMincludes Saudi Arabian volcanic ash, water, XC polymer, psyllium huskpowder, Class H Portland cement, sodium hydroxide, and a de-foamer. Insome embodiments of the present invention, the drilling mud used in themethod of the present invention includes volcanic ash, water, a pHbuffer, de-foamer, a viscosifier, a fluid loss control additive, and abinder.

In at least one embodiment of the present invention, the composition ofthe gel-based LCM is formulated to achieve a target gel characteristicin the lost circulation zone. Exemplary target gel characteristicsinclude a gel breaking strength (lb/100 ft²), a gel stiffness modulus(lbf/mm), a yield strength (lbf), and combinations thereof. The gelbreaking strength indicates the load suspension capability of agel-based LCM. Load suspension capability is a marker of the ability ofa gel-based LCM to affect a lost circulation zone. The higher the gelbreaking strength, the higher the load suspension capability and themore likely the gel-based LCM is capable of altering a massive lostcirculation zone. The gel stiffness modulus is indicative of theresistance of a gel to flow when subjected to a moving force. In awellbore, the gel stiffness modulus indicates the gel resistance to flowwhile being squeezed into the lost circulation zone. The higher the gelstiffness modulus, the greater the resistance to flow in the fracturesand permeable channels, leading to partial or complete blockage of thelost circulation zone. The yield strength indicates the force necessaryto initiate flow of the gel associated with plastic deformation. Thehigher the yield strength of a gel-based LCM, the greater resistance toflow of the gel-based LCM in the fractures and permeable channels of thewellbore, while the gel is forced into a lost circulation zone.Resistance to flow translates to a composition that will readilysolidify, within the lost circulation zone. The solidified gel-based LCMcreates an effective flow barrier to stop fluid/mud losses in the lostcirculation zone.

The target gel characteristic is determined based on the nature of thelost circulation zone. Without being bound to a particular theory, theweight ratio of the volcanic ash to the binder governs the target gelcharacteristic in the gel-based LCM, making both the presence of thebinder and the concentration of the binder critical to achieving thetarget gel characteristic. The weight ratio of the volcanic ash to thebinder is in the range from about 1:0.5 to about 1:5, alternately fromabout 1:1 to about 1:5, and alternately from about 1:1.5 to about 1:3.

Methods to use the gel-based LCM to control lost circulation in the lostcirculation zone in the wellbore are provided.

Embodiments Related to a Continuous Drilling Method for Delivering theGel-Based LCM

A continuous drilling method to control lost circulation in the lostcirculation zone in the wellbore during continuous drilling with thedual-purpose drilling mud is provided. The continuous drilling methodoccurs during the course of continuous drilling with the dual-purposedrilling mud from a surface down the wellbore. The term “dual-purposedrilling mud” as used herein signifies a fluid that can be used for twopurposes, that is, the fluid is useful as a drilling fluid and as acomponent of a lost circulation material as will be described herein.

As the wellbore is drilled, dual-purpose drilling mud is continuouslypumped into the wellbore to clear and clean the wellbore and thefilings. The dual-purpose drilling mud is pumped from a mud pit into thewellbore and returns again to the surface. In some embodiments of thepresent invention, the dual-purpose drilling mud that returns to thesurface is cleaned prior to being returned to the mud pit. Thedual-purpose drilling mud includes volcanic ash, water, a viscosifier, afluid loss control additive, a pH buffer, and de-foamer.

Drilling proceeds until a lost circulation zone is encountered. A lostcirculation zone is encountered when the flow rate of the dual-purposedrilling mud that returns to the surface is less than the flow rate ofthe dual-purpose drilling mud pumped into the wellbore.

The lost circulation zone is characterized by estimating the lostcirculation volumetric flow rate. The lost circulation volumetric flowrate is the rate at which the dual-purpose drilling mud is lost in thelost circulation zone. In at least one embodiment of the presentinvention, the lost circulation volumetric flow rate is estimated basedon the drop of level in a mud tank. The mud tank is the point of originand return for the dual-purpose drilling mud. In at least one embodimentof the present invention, the lost circulation volumetric flow rate isestimated based on the difference between the flow rate of thedual-purpose drilling mud pumped into the wellbore and the flow rate ofthe dual-purpose drilling mud that returns to the surface. “Estimate” orvariations thereof, as used herein, includes determining or calculatingthe lost circulation volumetric flow rate, estimates are appropriatebecause the exact lost circulation volumetric flow rate is not requiredto proceed with the method of the present invention. Any methods forestimating the flow rate of the dual-purpose drilling mud pumped intothe wellbore and the flow rate of the dual-purpose drilling mud thatreturns to the surface is appropriate. In at least one embodiment of thepresent invention, flow meters are used to estimate the flow rates.

The lost circulation volumetric flow rate is any value greater than zero(0) but less than the flow rate of the dual-purpose drilling mud pumpedinto the wellbore. In at least one embodiment of the present invention,the lost circulation volumetric flow rate is any value greater than 10bbsls/hr but less than the flow rate of the dual-purpose drilling mudpumped into the wellbore. A loss of 10 bbl/hr of the dual-purposedrilling mud is expected due to adherence to rock cuttings and smallincreases in hole volume. The lost circulation volumetric flow rate isanalyzed to identify the nature of the lost circulation zone. The largerthe lost circulation volumetric flow rate the larger the lostcirculation zone. The lost circulation zone can be a seepage type lostcirculation zone, a moderate type lost circulation zone, a severe lostcirculation zone, or any other type known to one of skill in the art.For example, a lost circulation volumetric flow rate near to the flowrate of the dual-purpose drilling mud pumped into the wellbore indicatesa large lost circulation zone. In some instances, the lost circulationvolumetric flow rate may approximate the flow rate of the dual-purposedrilling mud pumped into the wellbore indicating a massive lostcirculation zone.

In at least one embodiment of the present invention, the dual-purposedrilling mud is continuously pumped into the wellbore after a lostcirculation zone is encountered.

Understanding the nature of the lost circulation zone providesinformation helpful to estimating the first amount of the binder to beadded to the dual-purpose drilling mud to create the gel-based LCM forcontrolling the lost circulation volumetric flow rate in the lostcirculation zone. The addition of the first amount of the binder to thedual-purpose drilling mud creates a binder containing dual-purposedrilling mud. The gel-based LCM is created when the binder containingdual-purpose drilling mud achieves the target gel characteristic.

The first amount of the binder can be determined based on considerationsof the flow rate of the dual-purpose drilling mud pumped into thewellbore, the distance to the lost circulation zone, the lostcirculation volumetric flow rate, the nature of the lost circulationzone, and the target gel characteristic.

In at least one embodiment of the present invention, the first amount ofthe binder is selected from a pre-selected range. The pre-selected rangeis a function of the amount of volcanic ash in the dual-purpose drillingmud such that the pre-selected range encompasses the weight ratio of thevolcanic ash to binder needed to achieve the target gel characteristic.

In at least one embodiment of the present invention, the first amount ofthe binder is determined from estimating a gel-based LCM volume. Thegel-based LCM volume is estimated by multiplying the lost circulationvolumetric flow rate by the lost time. The lost time is any unit oftime, such that multiplying the lost circulation volumetric flow rate bythe lost time will result in a volume. The lost time can be about 30minutes, alternately greater than about 30 minutes, alternately aboutone hour, alternately about two hours, alternately about three hours,alternately about four hours, alternately between about 2 and about 5hours, and alternately by more than about 5 hours. The lost time isselected in consideration of the nature of the lost circulation zone,where a higher lost time value is used for more severe lost circulationzones. In at least one embodiment of the present invention, a time abovetwo hours will be selected for a lost circulation of a moderate type orsevere type lost circulation zone. The amount of binder is selected toproduce the gel-based LCM volume as estimated. In some embodiments ofthe present invention, multiplying the lost circulation volumetric flowrate by the lost time provides a gel-based LCM volume that is greaterthan the volume of dual-purpose drilling mud lost in one hour at thelost circulation volumetric flow rate lost.

In an alternate embodiment of the present invention, the first amount ofthe binder is selected in consideration of the target gelcharacteristic, such that the binder containing dual-purpose drillingmud achieves the target gel characteristic during contact with the lostcirculation zone. One of skill in the art will appreciate that if thetarget gel characteristic is achieved at a distance from the surface butbefore entering the lost circulation zone, then the binder containingdual-purpose drilling mud might gel up in the wellbore causing nodual-purpose drilling mud to reach the lost circulation zone.Conversely, if the target gel characteristic is achieved at a distancefrom the surface but after entering the lost circulation zone, then thebinder containing dual-purpose drilling mud will gel outside of the lostcirculation zone and have minimal effect on lost circulation. The firstamount of the binder is established based on the composition of thedual-purpose drilling mud prior to addition of the binder, such that thedesired weight ratio of the volcanic ash to the binder is achieved.

The first amount of the binder is then metered into the dual-purposedrilling mud to create the binder containing dual-purpose drilling mud,as the dual-purpose drilling mud is continuously being pumped into thewellbore. “Metering,” as used herein, means that the first amount of thebinder is added to the dual-purpose drilling mud over time and not as abatch addition. The rate at which the binder is metered into thedual-purpose drilling mud is commensurate with the need to achieve thetarget gel characteristic in the lost circulation zone. Considerationsof the flow rate of the dual-purpose drilling mud pumped into thewellbore, the distance to the lost circulation zone, and the target gelcharacteristic.

The binder containing dual-purpose drilling mud is pumped into thewellbore. The pump used in the pumping step is the same pump that isused to pump the dual-purpose drilling mud into the wellbore prior toentering the lost circulation zone. In at least one embodiment of thepresent invention, the pumping step is concurrent with the meteringstep.

After the pre-defined regulating period of time, metering of the firstamount of the binder into the dual-purpose drilling mud is suspended.The pre-defined regulating period of time ensures that binder containingdual-purpose drilling mud reaches the lost circulation zone and achievesthe target gel characteristic at the lost circulation zone to reduce thefirst lost circulation volume. The pre-defined regulating period of timeis between about 30 minutes and 6 hours, alternately between 1 hour and5 hours, alternately between 2 hours and 4 hours, alternately between 30minutes and 2 hours, alternately between 3 hours and 6 hours,alternately greater than 6 hours. The pre-defined regulating period oftime is effective to permit the binder containing dual-purpose drillingmud to achieve the target gel characteristic to create the gel-based LCMin the wellbore in the lost circulation zone.

After the binder containing dual-purpose drilling mud reaches the lostcirculation zone, pumping is suspended for a setting time. The settingtime is between 30 minutes and 3 hours, alternately between 1 hour and 2hours.

The gel-based LCM is operable to alter the lost circulation zone, suchthat the lost circulation volumetric flow rate is reduced and the flowrate of the dual-purpose drilling mud returned to the surface increases.“Alter,” as used herein, means that the lost circulation zone and thelost circulation volumetric flow rate is reduced, minimized, oreliminated. The gel-based LCM gels at the lost circulation zone creatinga blockage or plug which prevents the dual-purpose drilling mud fromleaving the wellbore. In at least one embodiment of the presentinvention, the gel-based LCM plugs off a portion of the lost circulationzone. In one embodiment of the present invention, the gel-based LCMplugs off the entire lost circulation zone, the flow rate to the surfaceresumes or reaches a level equivalent to or nearly equivalent to theflow rate being pumped into the wellbore.

In certain embodiments, the method of the present invention includes thesecond lost circulation step occurring after suspension of the meteringof the first amount of the binder. The second lost circulationvolumetric flow rate is determined by estimation. The second lostcirculation volumetric flow rate is estimated based on the differencebetween the flow rate of the dual-purpose drilling mud pumped into thewellbore and the flow rate of the dual-purpose drilling mud that returnsto the surface. The second lost circulation volumetric flow rate is anyvalue greater than zero (0) but less than the flow rate of thedual-purpose drilling mud pumped into the wellbore. In at least oneembodiment of the present invention, the lost circulation volumetricflow rate is any value greater than 10 bbls/hr but less than the flowrate of the dual-purpose drilling mud pumped into the wellbore. A lossof 10 bbl/hr of the dual-purpose drilling mud is expected due toadherence to rock cuttings and small increases in hole volume. In someembodiments, the second lost circulation volumetric flow rate will beless than the lost circulation volumetric flow rate. In at least oneembodiment, the second lost circulation volume will be greater than thelost circulation volumetric flow rate. The second lost circulation stepis necessary when the lost circulation zone is still considered to belarge as determined by an estimate of the lost circulation volumetricflow rate and the nature of the lost circulation zone as determinedherein.

In the second metering step, a second amount of the binder is meteredinto the dual-purpose drilling mud. The second amount of the binder isdetermined as described above with reference to the first amount of thebinder. The second amount of the binder is metered into the dual-purposedrilling mud while the dual-purpose drilling mud is continuously pumpedinto the wellbore as described above with reference to metering thefirst amount of the binder. After the pre-defined regulating period oftime, the metering of the second amount of the binder is suspended.

In at least one embodiment of the present invention, the continuousdrilling method to control lost circulation in the lost circulation zonein the wellbore during continuous drilling with the dual-purposedrilling mud can be repeated until the lost circulation zone is alteredby the gel-based LCM.

In an alternative embodiment of the present invention, the methodincludes a mixing step. In the mixing step, the binder is mixed with thedual-purpose drilling mud following the metering step. The mixing stepcan occur in any mixer capable of mixing the dual-purpose drilling mudand the first amount of the binder. In one embodiment of the presentinvention, the mixing step occurs in a mixer downstream of the mud pit,but upstream of the pump that pumps the dual-purpose drilling mud orbinder containing dual-purpose drilling mud into the wellbore.

In some embodiments of the present invention, the dual-purpose drillingmud of the method is created by mixing volcanic ash, water, thede-foamer, the pH buffer, the viscosifier, and the fluid loss controladditive to create the dual-purpose drilling mud. The dual-purposedrilling mud is configured to be pumped into the wellbore. The step tocreate the binder containing dual-purpose drilling mud includes addingthe binder to the dual-purpose drilling mud at the drilling site duringcontinuous pumping of the dual-purpose drilling mud into the wellbore.

The gel-based LCM that has achieved target gel characteristics isunsuitable for use as a dual-purpose drilling mud. The dual-purposedrilling mud of the present invention is formulated to react with thebinder to achieve the gel-based LCM. The binder containing dual-purposedrilling mud is in the absence of solidified dual-purpose drilling mud.

Embodiments Related to a Pill-Based Method for Delivering the Gel-BasedLCM

A pill-based method for altering the lost circulation volumetric flowrate in a lost circulation zone is provided. In the pill-based method ofthe present invention, a gel-based LCM pill is introduced to the lostcirculation zone to alter the lost circulation volumetric flow rate,wherein the gel-based LCM is created when the gel-based LCM pillachieves the target gel characteristic. The pill-based method of thepresent invention can be used to control the lost circulation volumetricflow rate regardless of the drilling fluid being used to drill thewellbore.

During the drilling stage, drilling fluid is pumped into the wellboreuntil the lost circulation zone is entered. In at least one embodimentof the pill-based method, the drilling fluid is in the absence of thedual-purpose drilling mud. As described herein, the lost circulationzone is entered when the flow rate of the drilling fluid that returns tothe surface is less than the flow rate of the drilling fluid pumped intothe wellbore.

Once a lost circulation zone is entered, the lost circulation volumetricflow rate is estimated. The lost circulation volumetric flow rate isestimated based on the difference between the flow rate of the drillingfluid pumped into the wellbore and the flow rate of the drilling fluidthat returns to the surface as described herein. The lost circulationvolumetric flow rate is analyzed to identify the nature of the lostcirculation zone as described herein. The nature of the lost circulationzone allows one to estimate the lost time as described herein. Thevolume of the gel-based LCM pill is estimated by multiplying the losttime by the lost circulation volumetric flow rate. The volume of thegel-based LCM pill is an estimate of the volume of the gel-based LCMexpected to be required to alter the lost circulation volumetric flowrate.

The gel-based LCM pill is produced by mixing the volcanic ash, thewater, the viscosifier, the fluid loss control additive, the pH buffer,the defoamer, and the binder. The gel-based LCM pill is produced bymixing the components in the quantities to achieve the volume estimated.The quantity of each component, including the amount of binder, isselected based on the target gel characteristic, the distance to thelost circulation zone, the lost circulation volumetric flow rate, andthe nature of the lost circulation zone. In at least one embodiment, thevolcanic ash, the water, the viscosifier, the fluid loss controladditive, the pH buffer, and the defoamer are pre-mixed, that is thecomponents are mixed prior to such as time as entering a lostcirculation zone. The gel-based LCM pill can be mixed in any mixingvessel suitable for mixing a pill to be delivered downhole. In at leastone embodiment of the present invention, the gel-based LCM is mixed in ahopper connected by valve to the open end pipe.

The drilling stage is suspended after entering the lost circulationzone. Suspension of the drilling stage can occur as soon as the lostcirculation zone is entered, while the gel-based LCM pill is beingmixed, or after the gel-based LCM pill is mixed.

Delivery of the gel-based LCM pill is facilitated by the open end pipe.The open end pipe is aligned between the surface and the lostcirculation zone in proximity to the lost circulation zone. The open endpipe can be any kind of downhole pipe capable of deliver the gel-basedLCM to the lost circulation zone. In at least one embodiment of thepresent invention, the drill bit is retracted to a position between thesurface and the lost circulation zone.

Once the open end pipe is placed, the gel-based LCM pill is pumped atthe pill pump rate. The pill pump rate delivers the gel-based LCM pillto the lost circulation zone at a rate to avoid the gel-based LCM pillachieving the target gel characteristic in the open ended pipe. The pillpump rate is greater than 10 bbl/min, alternately between about 0.5bbl/min and about 10 bbl/min, alternately between about 1 bbl/min andabout 5 bbl/min, and alternately between about 2 bbl/min and about 3bbl/min. In at least one embodiment of the present invention, the pillpump rate is pre-determined prior to entering a lost circulation zone.

After the entire volume of the gel-based LCM pill has been pumped intothe open end pipe, the displacing mud is pumped into the open end pipeat the displacement rate. The displacement rate displaces the gel-basedLCM pill from the open end pipe, so that the gel-based LCM pill isplaced in the lost circulation zone when it achieves the target gelcharacteristic. In at least one embodiment of the present invention, thedisplacement rate is pre-determined prior to entering the lostcirculation zone. The displacement rate can be determined based on thepill pump rate, the length of the open end drill pipe, and thedisplacing mud.

Once the displacement mud displaces the gel-based LCM pill from the openend pipe, the wellbore is shut for the gelling time. The gelling timeaffords the gel-based LCM pill time to achieve the target gelcharacteristic to form the gel-based LCM in the lost circulation zone.In at least one embodiment of the present invention, the gelling time isdetermined based on the amount of binder in the volume of the gel-basedLCM pill and the nature of the lost circulation zone. An exemplarygelling time is between 30 minutes and 5 hours, between 1 hour and 4hours, between 2 hours and 3 hours. In at least one embodiment of thepresent invention, the gelling time is 2 hours.

At the end of the gelling time, the wellbore is opened and the drillingfluid is pumped into the open end drill pipe. The return rate ofdrilling fluid can be measured and a lost circulation volumetric flowrate can be determined. If the lost circulation volumetric flow rate isgreater than zero, the gel-based LCM pill based method for altering alost circulation zone is repeated. In at least one embodiment of thepresent invention, if the lost circulation volumetric flow rate isgreater than 10 bbls/hr, the gel-based LCM pill based method foraltering a lost circulation zone is repeated. In at least one embodimentof the present invention, drilling fluid is pumped into the wellbore anda pressure of the wellbore is measured. When the measured pressure ismaintained for a period of time, normal operations commence. If themeasured pressure is not maintained for a period of time, the gel-basedLCM pill-based method is repeated.

EXAMPLES Example 1

In example 1, three different samples of the gel-based LCM were created,Table 1. The volcanic ash was a Saudi Arabian volcanic ash (SAVA). Theviscosifier was XC polymer. The viscosifier was a pysllium husk powder(PHP). The pH buffer was sodium hydroxide. The de-foamer was BARABRINE®defoam. The binder was a class H cement. Each sample contained adifferent amount of the binder added to a prepared dual-purpose drillingmud. Each sample was mixed for 20 minutes using a variable speedHamilton Beach mixer. A standard rotational viscometer was used tomeasure the rheological and gel strength properties of the resultinggel-based LCM sample, Table 2. The rotational viscometer readings weretaken at room temperature and atmospheric pressure. The rotationalviscometer was used to assess the inter-particle bond strength of themixture after aging periods of 10 minutes, 1 hour, and 2 hours (Table3). After the two hour aging period, a suspended weight test wasperformed as a second comparative evaluation of gel stiffness, seeFIG. 1. Discs were placed onto samples of the gel-based LCM and wereobserved to determine the ability of the gel to suspend the weight.Discs weighing between 100 and 500 grams were used.

TABLE 1 Composition of the Samples Components SAMPLE 1 SAMPLE 2 SAMPLE 3Water (ml) 350 350 350 SAVA -I (g) 20 20 20 XC Polymer (g) 3 3 3 PHP 95(g) 3 3 3 NaOH (ml) as required as required as required to raise toraise to raise pH 10 pH 10 pH 10 De-Foamer (cc) as required as requiredas required Cement (g) 0 30 60

TABLE 2 Dial Readings and Gel Strength of Sample 1 Rotational Speed(rpm) Gel Strength 600 300 200 100 6 3 10 Seconds 10 Minutes GelStrength Gel Strength Dial Reading lbs/100 ft² lbs/100 ft² 67.8 59 56.750 32 31 29.8 33.6

TABLE 3 Gel Breaking Strength Sample Gel Breaking Force (Lbs/100 ft²)Aging Time SAMPLE 1 SAMPLE 2 SAMPLE 3 10 Seconds 29.8 31.1 36.7 StaticAging 1 Hour 30.3 105.4 124.6 Static Aging 2 Hour 31.7 142 Beyond StaticAging Measurable Range

Results

Sample 1 represented a composition of the dual-purpose drilling mudwithout the binder. The results in Table 2 indicate that Sample 1 issuitable for use as the dual-purpose drilling mud because of the flatgel properties make for good cuttings suspension. The results alsoindicate weak inter-particle bonds easily breakable by an externalforce. During the suspended weight test, the 100 gram disc sankimmediately into the dual-purpose drilling mud, after placement of thedisc on top of the mud as shown in FIG. 1(a). The suspended weight testconfirms that the dual-purpose drilling mud has poor structural rigidityand is not a well gelled mud system.

The composition of Sample 2 with the binder produces the bindercontaining dual-purpose drilling mud. Table 3 shows that the addition ofthe binder converts the dual-purpose drilling mud to a gel-based LCM andprovides values for a target gel characteristic of the gel breakingstrength. When compared to Sample 1, Sample 2 shows enhanced gelbreaking strength with increasing aging time. The suspended weight testconfirmed that the gel-based LCM exhibited a gel stiffness greater thanthe dual-purpose drilling mud. When the 100 gram disc was placed onSample 2, the disc sank more slowly than it had during the test ofSample 1 as shown in FIG. 1(b). The disc still sank, suggesting thatwhile some inter-particle bonds had been created, the Sample 2 gel-basedLCM was not a well gelled mud system with low load suspension capabilitydue to insufficient target gel characteristics.

Sample 3 is an example of a composition useful to produce a gel-basedLCM. Table 3 shows that when compared to Samples 1 and 2, Sample 3exhibited enhanced gel breaking strength with increasing aging time.After 2 hours of aging, the rotational viscometer was unable to measurethe gel breaking strength of Sample 3 because the gel breaking strengthwas beyond the measurement range of the rotational viscometer. It issuspected that Sample 3 developed strong inter-particle bonds in the gelsystem during the aging period thus producing the gel-based LCM. Duringthe suspended weight test, the 100 gram disc did not sink into Sample 3,see FIG. 1(c). Then, 200, 300, and 500 gram discs were placed on top ofSample 3, see FIGS. 1(d), (e), and (f). Again, the 200 and 300 gramdiscs did not appreciably sink into Sample 3. Even the 500 gram disc didnot fully sink into Sample 3. Sample 3 shows significant load suspensioncapability, indicating effective conversion of the dual-purpose drillingmud to a gel-based LCM.

The data for samples 2 and 3 indicate highly progressive target gelcharacteristics for a gel-based LCM.

Example 2

In Example 2, samples of the gel-based LCM and samples of conventionalLCMs were subjected to compression tests for comparison. The componentsand composition for each sample are shown in Table 4. The conventionalLCMs, samples G and H, were prepared using two different commerciallyavailable water soluble polymers ZND-2 and ZND-6. To prepare thesamples, the components of each sample were mixed together for 20minutes using a variable speed (rpm) Hamilton Beach mixer. The sampleswere cured for two hours in a closed container to allow time forinter-particle bonding, networking, and gel stiffening. The compressiontests were performed using a test cell that included a perforated discconnected to a computer and program that displayed the resultselectronically. The test cell ensured the same volume of sample was usedin each compression test. All the samples were tested under the sameconditions, compression test type with a pre-test speed of 1.0 nm/sec, atest speed of 1.0 m/sec, a post-test speed of 10.0 mm/sec and a distanceof 40 mm. The test speed is a measure of the flat foot disc displacementthat was used to push the top of the samples resting in the test cell.For each sample, three runs were performed to determine an average valuefor each sample.

The results were displayed graphically as a plot of displacement (mm)versus compression force (lb). The plots were then used to determine thetarget gel characteristics of gel stiffness modulus and the yieldstrength of the samples. The gel stiffness modulus is the slope of theintermediate part of the rising flanks of the curve, i.e., theintermediate linear part of the curve. The yield strength is thecompression force (the peak of the curve) at which flow of the samplewas initiated through the perforations of the bottom disc of the testcell. FIGS. 2-5 contain the graphical results in a plot of displacement(mm) versus compression force. Table 5 contains the gel stiffnessmodulus and the yield strength for each sample, including the average.

TABLE 4 Composition of the Samples Components SAMPLE E SAMPLE F SAMPLE GSAMPLE H Water (ml) 350 350 345.8 345.8 SAVA -I (g) 20 20 — — XC Polymer3 3 — — (g) PHP 95 (g) 3 3 — — NaOH (ml) as required as required — — toraise to raise pH 10 pH 10 De-Foamer as required as required — — (cc)Cement 30 60 — Water Soluble — — 4.2 (ZND-2) 4.2 (ZND-6) Polymer (g)

TABLE 5 Experimentally Determined Gel Stiffness Modulus and YieldStrength Gel Stiffness Yield Strength LCM Systems Module (lbf/mm) (lbf)Sample E, Run 1 8.461 17.561 Sample E, Run 2 11.63 16.501 Sample E, Run3 11.46 16.46 Sample E Average 10.52 16.84 Sample F, Run 1 28.602 94.26Sample F, Run 2 27.414 92.538 Sample F, Run 3 21.934 90.187 Sample FAverage 25.98 92.33 Sample G, Run 1 0.123 0.423 Sample G, Run 2 0.1110.434 Sample G, Run 3 0.196 0.439 Sample G Average 0.143 0.432 Sample H,Run 1 0.213 0.496 Sample H, Run 2 0.231 0.332 Sample H, Run 3 0.2330.609 Sample H Average 0.226 0.479

FIG. 6 is a graphical comparison of the average gel stiffness modulusfor each of the samples. The average data indicate that the average gelstiffness modulus of Sample E was more than 7000% higher than theaverage gel stiffness modulus of Sample G and more than 4000% higherthan Sample H. The average data indicate that the average gel stiffnessmodulus of Sample F was more than 18000% higher than the average gelstiffness modulus value of Sample C and more than 11000% higher thanSample H. The high gel stiffness modulus of Samples F and G indicatethat Samples F and C offer greater resistance to flow than Samples G andH. The greater resistance to flow means that the composition of samplesF and G, the gel-based LCM of the present invention, provides a bettersolution for moderate type to severe type lost circulation.

FIG. 7 is a graphical representation of the average yield strength foreach of the samples. An analysis of the average yield strength value ofSample E indicates an average yield strength more than 3500% higher thanSample G and more than 3000% higher than Sample H. The average dataindicate that the average yield strength of Sample F was more than21000% higher than Sample G and about 19000% higher than Sample H. Theaverage yield strength data suggest that the formulations of Samples Eand F have extremely high yield strength properties compared to SamplesG and H. The average data indicate that the yield strength of Sample Fwas greater than the yield strength of Sample E. A comparison of SampleE to Sample F indicates that the amount of binder can be modified toachieve a desired yield strength.

The present invention may suitably comprise, consist or consistessentially of the elements disclosed and may be practiced in theabsence of an element not disclosed. For example, it can be recognizedby those skilled in the art that certain steps can be combined into asingle step.

Unless defined otherwise, all technical and scientific terms used havethe same meaning as commonly understood by one of ordinary skill in theart to which this invention belongs.

The singular forms “a,” “an,” and “the” include plural referents, unlessthe context clearly dictates otherwise.

As used herein and in the appended claims, the words “comprise,” “has,”and “include” and all grammatical variations thereof are each intendedto have an open, non-limiting meaning that does not exclude additionalelements or steps.

“Optionally” means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions, and alterations canbe made hereupon without departing from the principle and scope of theinvention. Accordingly, the scope of the present invention should bedetermined by the following claims and their appropriate legalequivalents.

What is claimed is:
 1. A method to control lost circulation in a lostcirculation zone in a wellbore during continuous drilling with adual-purpose drilling mud, the method comprising the steps of:encountering the lost circulation zone, the lost circulation zone beingwhere a flow rate of the dual-purpose drilling mud that returns to asurface is less than a flow rate of the dual-purpose drilling mud pumpedinto the wellbore, wherein the dual-purpose drilling mud comprises avolcanic ash, water, a de-foamer, a pH buffer, a viscosifier, and afluid loss additive; estimating a lost circulation volumetric flow rate,the lost circulation volumetric flow rate being defined as a differencebetween the flow rate of the dual-purpose drilling mud pumped into thewellbore and the flow rate of the dual-purpose drilling mud that returnsto the surface; metering a first amount of a binder into thedual-purpose drilling mud to create a binder containing dual-purposedrilling mud, wherein the first amount of the binder metered is in apre-selected range based on a target gel characteristic, such that thefirst amount of the binder metered is operable to achieve the target gelcharacteristic of the binder containing dual-purpose drilling mud,wherein a weight ratio of the volcanic ash to the binder is 1:1.5 to1:3, wherein the binder is selected from the group consisting ofdrilling grade cements of Class A, Class B, Class C, Class G, Class H orcombinations thereof; pumping the binder containing dual-purposedrilling mud into the wellbore; and suspending metering of the firstamount of the binder to the dual-purpose drilling mud after apre-defined regulating period of time, wherein the pre-definedregulating period of time is effective to permit the binder containingdual-purpose drilling mud to achieve the target gel characteristic tocreate a gel-based lost circulation material (LCM) for contact with thelost circulation zone, the gel-based LCM being operable to alter thelost circulation zone, such that the flow rate of the dual-purposedrilling mud that returns to the surface increases.
 2. The method ofclaim 1 further comprising the steps of: estimating a second lostcirculation volume, the second lost circulation volume being defined asa difference between the flow rate of the dual-purpose drilling mudpumped into the wellbore after the step of suspending metering of thefirst amount of the binder and the flow rate of the dual-purposedrilling mud that returns to the surface; metering a second amount ofthe binder into the dual-purpose drilling mud, wherein the second amountof the binder metered is in a pre-selected range based on the target gelcharacteristic; and suspending metering of the second amount of thebinder.
 3. The method of claim 1 further comprising the step of: mixingthe first amount of the binder with the dual-purpose drilling mud in aseparate mixing step following the step of metering the first amount ofthe binder into the dual-purpose drilling mud.
 4. The method of claim 1,wherein the pH buffer is selected from the group consisting of sodiumhydroxide, potassium hydroxide, and lime.
 5. The method of claim 1,wherein the viscosifier is XC polymer.
 6. The method of claim 1, whereinthe fluid loss control additive is psyllium husk powder.
 7. The methodof claim 1, wherein the pre-defined regulating period of time is between30 minutes and 2 hours.
 8. The method of claim 1, wherein the target gelcharacteristic is selected from the group consisting of a gel breakingstrength, a gel stiffness modulus, a yield strength, and combinationsthereof.